Individuals who loose all or part of a leg have a residual limb to which a prosthetic foot is often attached using a mounting pylon. The attachment between the lower end of the pylon and the prosthetic foot approximates an ankle joint. However, in the past, pylons have been rigidly attached to prosthetic feet thus creating a rigid ankle joint. Rigid ankle joints have typically relied on the cushion in the heel of the prosthetic foot to allow relative axial motion between the residual limb and the ground. However, this approach has proven to be inadequate because it makes the individual walk awkwardly, and prone to stumble when standing on an incline.
The basic problem with the rigid ankle joint is that it does not mimic a real ankle. As a result, prosthetic designers have developed pivotal ankle joints. Such ankle joints may provide some motion in three potential orthogonal planes, namely the sagital, coronal, and transverse planes. The sagital plane is a vertical front-to-back plane and movement in the sagital plane is known as either dorsi-flexion in which the toe pivots upwardly or plantar flexion in which the toe pivots downwardly.
When an artificial foot is attached to an artificial limb, the initial alignment and adjustment fixes the heel height to a particular shoe and the user must continue to wear shoes that have identical heel heights. This often requires the amputee to wear the same model of shoe always. If a different shoe is worn the stability of the prosthesis is affected resulting in an unnatural gait and in some cases an unsafe limb. While the leg member can be subsequently disassembled, realigned and adjusted for a different heel height and again fitted to the user, this is a cumbersome process, and again the prosthesis is limited to a fixed prosthetic member.
The advantage of a prosthetic leg having a foot member with an adjustable heel height can be readily appreciated. The user can manually adjust the heel height of the foot member to an optimum position for comfort and safety for the particular shoes that he/she is wearing. The adjustment capability allows the amputee with minor training to self adjust for any heel height chose. The amputee is then afforded a wide variety of shoes from heelless slippers to high heel boots.
Accordingly, there is a need for an ankle joint prosthesis which allows self adjustment by the wearer of the heel height depending upon the shoes which are used in combination with the artificial foot and/or the terrain that the amputee is walking on.